feat(FN-4813): complete Step 5 — add isolation transition runtime restart path

Fusion-Task-Id: FN-4813
Fusion-Task-Lineage: 846893a5-2afa-4817-8f64-8c444d2fd713

packages/core/src/__tests__/project-isolation-transition.test.ts

@@ -0,0 +1,53 @@
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { mkdirSync, mkdtempSync } from "node:fs";
+import { rm } from "node:fs/promises";
+import { join } from "node:path";
+import { tmpdir } from "node:os";
+import { CentralCore } from "../central-core.js";
+
+describe("CentralCore.transitionProjectIsolation", () => {
+  let tempDir: string;
+  let projectPath: string;
+  let core: CentralCore;
+
+  beforeEach(async () => {
+    tempDir = mkdtempSync(join(tmpdir(), "fn-project-isolation-transition-"));
+    projectPath = join(tempDir, "project");
+    mkdirSync(projectPath, { recursive: true });
+    core = new CentralCore(tempDir);
+    await core.init();
+  });
+
+  afterEach(async () => {
+    await core.close();
+    await rm(tempDir, { recursive: true, force: true, maxRetries: 5, retryDelay: 50 });
+  });
+
+  it("returns noop when next mode matches existing mode", async () => {
+    const project = await core.registerProject({
+      name: "Test",
+      path: projectPath,
+      isolationMode: "in-process",
+    });
+
+    const result = await core.transitionProjectIsolation(project.id, "in-process");
+    expect(result).toEqual({ ok: false, reason: "noop" });
+  });
+
+  it("updates mode and logs activity on success", async () => {
+    const project = await core.registerProject({
+      name: "Test",
+      path: projectPath,
+      isolationMode: "in-process",
+    });
+
+    const result = await core.transitionProjectIsolation(project.id, "child-process");
+    expect(result).toEqual({ ok: true });
+
+    const updated = await core.getProject(project.id);
+    expect(updated?.isolationMode).toBe("child-process");
+
+    const activity = await core.getRecentActivity({ projectId: project.id, limit: 10 });
+    expect(activity.some((entry) => entry.type === "project:isolation-transition")).toBe(true);
+  });
+});

packages/core/src/central-core.ts

@@ -514,6 +514,40 @@ export class CentralCore extends EventEmitter<CentralCoreEvents> {
     return updated;
   }
 
+  async transitionProjectIsolation(
+    projectId: string,
+    nextMode: IsolationMode,
+    opts: { force?: boolean } = {}
+  ): Promise<{ ok: true } | { ok: false; reason: string; activeTaskCount?: number }> {
+    void opts;
+    this.ensureInitialized();
+
+    const project = await this.getProject(projectId);
+    if (!project) {
+      throw new Error(`Project not found: ${projectId}`);
+    }
+
+    if (project.isolationMode === nextMode) {
+      return { ok: false, reason: "noop" };
+    }
+
+    await this.updateProject(projectId, { isolationMode: nextMode });
+    await this.logActivity({
+      type: "project:isolation-transition",
+      projectId,
+      projectName: project.name,
+      timestamp: new Date().toISOString(),
+      details: `Project isolation mode transitioned: ${project.isolationMode} -> ${nextMode}`,
+      metadata: {
+        from: project.isolationMode,
+        to: nextMode,
+      },
+    });
+
+    return { ok: true };
+  }
+
+
   /**
    * Reconcile stale project statuses.
    *